Pressurized air system

ABSTRACT

A pressurized air system controls air pressure in air reservoirs that deliver compressed air to air-actuated components in a vehicle. An air compressor supplies compressed air to air reservoirs which deliver compressed air to air-actuated components. A control system measures the air pressure in the air reservoirs by using at least one electric switch. Each switch is connected to an air reservoir and generates an electric signal to an electrically controlled valve indicative of the measured air pressure in the corresponding air reservoir. The electrically controlled valve is connected to an air compressor. The electrically controlled valve moves between a first position causing the air compressor to supply compressed air to the air reservoirs and a second position causing the air compressor to stop supplying compressed air to the air reservoirs responsive to the received electronic signal.

CROSS REFERENCED TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Ser. No. 08/254,862,filed Jun. 6, 1994, now U.S. Pat. No. 5,533,866 and entitled"PRESSURIZED AIR SYSTEM".

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention pertains to a pressurized air system for vehicles and,more particularly, to a control system for regulating air pressure invehicle air reservoirs.

II. Description of the Prior Art

In the prior art, a particular embodiment of a pressurized air systemfor vehicles which controls the air pressure in air reservoirs between apredetermined maximum air pressure and a predetermined minimum airpressure, by use of an air governor, is well known. Air governors arecommonly used in trucks to control air pressures in air reservoirs whichdeliver air to service brakes and other air-actuated components.

In a typical embodiment of the prior art as implemented in a truckhaving a tandem and possibly a trailer, the air governor is connected toa supply reservoir (also known as a "wet tank"). The supply reservoir isan air reservoir connected in parallel with a primary air reservoir anda secondary air reservoir. Generally, one air reservoir is connectedonly to service brakes on the tandem and the trailer. The other airreservoir may be connected to front brakes, parking brakes, windshieldwipers and other air-actuated components.

The air pressure from the supply reservoir enters the air governor andacts on a piston and an inlet\exhaust valve. As air pressure in thesupply reservoir increases to the predetermined maximum air pressure, aninlet passage of the air governor opens, allowing air pressure to flowthrough the inlet passage and to an air compressor unloading mechanism.The flow of air to the air compressor unloading mechanism causes the aircompressor to stop compressing air. As air pressure in the supplyreservoir decreases to the predetermined minimum air pressure, the inletpassage closes and the exhaust opens, allowing air in the unloadingmechanism to escape back through the air governor and out of an exhaustport. The release of air from the unloading mechanism actuates the aircompressor to compress air and supply compressed air to the supplyreservoir and the other air reservoirs.

The air governor is generally mounted to the air compressor, although itcan be remotely mounted. It is generally not mounted in the cab due toits noise and size. An example of such an air governor is the Bendix D-2Governor, No. SD-01-16, Service Date Jul. 1984.

While the air governor such as described has proven to be useful in theindustry, it has several disadvantages. When mounted to the aircompressor or elsewhere in the engine compartment, the air governor isexposed to excessive vibration from the engine, dirt, extremetemperature fluctuations, moisture and other problematic externalparameters. Because of the air governor's numerous moving parts andcontinued exposure to external parameters while in operation, the airgovernor fails frequently and unpredictably. When the air governorfails, service brakes can lock up and other air-actuated components canstop working. In addition, maintenance and trouble-shooting aredifficult due to the frequent, unpredictable failure of parts and thelarge number of small high tolerance moving parts within the airgovernor. Finally, the air governor measures system air pressure fromthe supply reservoir which receives air directly from the aircompressor, rather than measuring the actual air pressure in the airreservoirs that provide air to the air-actuated components. Air pressurefrom the supply reservoir is not always a reliable measure of airpressure in the primary and secondary reservoirs due to leaks downstreamfrom the supply reservoir.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, apressurized air system for controlling air pressures in air reservoirswhich deliver compressed air to air-actuated components in a vehicle isdisclosed. The pressurized air system operates effectively with at leastone air reservoir. In the preferred embodiment, however, an aircompressor is connected to two air reservoirs and supplies compressedair to the air reservoirs when the air compressor is actuated. The airreservoirs are connected to air-actuated components such as, forexample, service brakes, parking brakes, and windshield wipers. Inanother embodiment, the air compressor is connected to a supplyreservoir which is connected to the air reservoirs.

A control system measures the air pressures in the air reservoirs andactuates the air compressor to compress air and supply compressed air tothe air reservoirs when air pressure in at least one of the airreservoirs decreases to at least a predetermined minimum air pressure,and disengages the air compressor to stop compressing air when airpressures in both of the air reservoirs increase to at least apredetermined maximum air pressure. In one embodiment, the controlsystem includes two switches, each being connected to one air reservoir,and an actuator. The actuator consists of a valve and an electric valvesetter for moving the valve between a first position and a secondposition. The switches respond to the changing air pressures in theircorresponding air reservoirs. The switches are electrically connected tothe electric valve setter. The actuator is operatively connected to theair compressor. When air pressure in at least one of the reservoirsdecreases to at least the predetermined minimum air pressure, thecorresponding switch(es) sends an electric signal to the actuator. Theelectric signal causes the electric valve setter to move the valve tothe first position, allowing air to escape from an unloading mechanismback through the valve, which actuates the air compressor to compressair. When air pressures in both reservoirs increase to at least thepredetermined maximum, neither switch generates an electric signal. Theabsence of an electric signal causes the electric valve setter to movethe valve to the second position, forcing air to flow into the unloadingmechanism, which disengages the air compressor to stop compressing air.

In another embodiment of the present invention, the air compressor isconnected to a supply reservoir, which is connected to at least one airreservoir. The air reservoir supplies air to air-actuated components.The control system is operatively connected to the supply reservoir formeasuring air pressure from the supply reservoir, rather than measuringair pressure from the air reservoir that provides air to air-actuatedcomponents. In this embodiment, the control system consists of only oneswitch connected to an actuator. The basic operation of the controlsystem in this embodiment remains the same. However, the switchgenerates an electric signal in response to air pressure changes in thesupply reservoir, rather than the air reservoirs that provide air toair-actuated components.

It is an object of the present invention to provide a reliablepressurized air system that is not prone to unpredictable failures andbreakdowns and that minimizes service brakes locking up.

It is a further object of the present invention to provide a pressurizedair system that is easy to maintain, with easy access to the controlsystem for trouble-shooting and repair work.

It is another object of the present invention to provide electricalcontrol of the pressurized air system using electrical switchesresponsive to air pressures in the individual air reservoirs.

It is an object of one embodiment of the present invention to provideelectrical control of the pressurized air system based upon air pressurelevels sensed directly from the air reservoirs that provide air toair-actuated components.

It is an object of another embodiment of the present invention toprovide electrical control of the pressurized air system based upon airpressure levels sensed from a supply reservoir.

It is yet a further object of the present invention to allow simpleconversion from the prior art to an embodiment of the present invention.

While the present invention is described in association with aparticular type of switch, the invention is not limited to the use ofsuch a switch as described. Further, while the invention is described inassociation with a particular type of actuator, it is to be understoodthat the invention is not limited to the use of such an actuator asdescribed. It will be known that the invention applies to a controlsystem wherein the actuator controls the operation of the air compressorusing air or a mechanical method, or the like. For example, amechanically controlled air compressor may include an air compressorwith a diverter valve wherein the air compressor continually compressesair. When the air pressure in at least one of the air reservoirsdecreases to at least a predetermined minimum air pressure, the controlsystem closes the diverter valve so that the compressed air generated bythe air compressor is forced to flow through the system to the airreservoirs. When air pressures in both of the air reservoirs increase toat least a predetermined maximum air pressure, the control system opensthe diverter valve so that the compressed air generated by the aircompressor is released from the system.

While the invention is described with reference to two reservoirs forcontrolling air-actuated components, the invention operates effectivelywith any number of reservoirs. Finally, while the invention is describedwith reference to a particular configuration of an electrical controlsystem, it is to be understood that the invention is not limited to sucha control system or wiring convention and it will be known that theinvention applies to other types of electrical control systems, such asa pressure sensor and microprocessor driven control system or the like.These and other features of the invention will become apparent to thoseskilled in the art upon a more detailed description of a preferredembodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a prior art pressurized airsystem utilizing an air governor.

FIG. 2 is a block diagram of one embodiment of the pressurized airsystem according to the present invention.

FIG. 3 is a schematic representation of one embodiment of thepressurized air system for controlling air pressures in the airreservoirs of a vehicle, according to the present invention and as shownin FIG. 2, with certain parts of the system shown in various alternativepositions.

FIGS. 4 and 4(a) through 4(d) schematically show the pressurized airsystem according to the embodiment shown in FIG. 2, at varying phasesduring operation.

FIG. 5 is a schematic representation of the pressurized air systemaccording to the embodiment shown in FIG. 2, as it is implemented in avehicle.

FIG. 6 is a schematic representation of an alternative embodiment of apressurized air system for controlling air pressures in air reservoirsof a vehicle, with certain parts of the system shown in variousalternative positions.

FIG. 7 is a block diagram of one preferred embodiment of the pressurizedair system according to the present invention.

DETAILED DESCRIPTION

In the following detailed description of the preferred embodiment,reference is made to the accompanying drawing which forms a part hereof,and in which is shown by way of illustration specific embodiments inwhich the invention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

FIG. 1 shows the structure of a pressurized air system 1 designed inaccordance with the prior art. Referring to FIG. 1, an air compressor 6is connected from an air compressor outlet 8 to a supply reservoir 12 byconduit 10. The supply reservoir 12 is connected to a first reservoir 20by conduit 14 and to a second reservoir 20' by conduit 16.

The first reservoir 20 is connected by conduit 24 to a first set ofair-actuated components 26. The second reservoir 20' is connected byconduit 24' to a second set of air-actuated components 26'. In the priorart, one set of air-actuated components consists of only service brakesand the other set of air-actuated components includes at least parkingbrakes, windshield wipers and front service brakes.

The supply reservoir 12 is also connected to an air governor 19 byconduit 18. The air governor 19 is connected to an unloading mechanism 4by an unloading mechanism conduit 2. The unloading mechanism is attachedto the air compressor 6 and controls the operation of the air compressor6. Use of an air compressor 6 with an unloading mechanism 4 is wellknown in the art.

Generally, the air compressor 6 compresses air and supplies compressedair through the compressor air outlet 8 into conduit 10 and to supplyreservoir 12. The compressed air then flows from the supply reservoir 12through conduit 14 to the first reservoir 20 and through conduit 16 tothe second reservoir 20'. The first reservoir 20 and the secondreservoir 20' provide compressed air to the first set of air-actuatedcomponents 26 and the second set of air-actuated components 26',respectively. The supply reservoir 12 continuously provides air to theair governor 19 through conduit 18. The operation of the air governor 19has previously been described herein. Generally, the air governor 19actuates the air compressor 6 to compress air, as previously describedherein, when air pressure in the supply reservoir 12 falls below apredetermined minimum air pressure. The air governor 19 disengages theair compressor 6 to stop compressing air, as previously describedherein, when air pressure in the supply reservoir 12 rises above apredetermined maximum air pressure.

FIG. 2 is a block diagram representation of one embodiment of thepressurized air system 30 according to the present invention. The aircompressor 36 is connected to a first reservoir 50 and a secondreservoir 50'. The first reservoir 50 and the second reservoir 50' areconnected to a first set of air-actuated components 56 and a second setof air-actuated components 56', respectively. Unlike the prior art, theair compressor 36 may be connected directly to the first reservoir 50and the second reservoir 50'. A supply reservoir, as shown in the priorart at 12, may be eliminated in the present invention. The firstreservoir 50 and the second reservoir 50' are connected to a controlsystem 60. The control system is operatively connected to the aircompressor 36 for actuating and disengaging the air compressor 36 inresponse to air pressure levels in the first reservoir 50 and the secondreservoir 50'. The control system 60 can control the operation of theair compressor 36 by air, mechanical means, or any other means in whichthe compressor is controlled to supply compressed air to the airreservoirs when needed and to stop the supply of compressed air to theair reservoirs when it is not needed.

FIG. 7 shows a block diagram representation of the pressurized airsystem 30 having a source of compressed air 39 connected to the firstreservoir 50 and the second reservoir 50'. The source of compressed aircan be any type of air compressor or other source of compressed air. Thecontrol system 60 is operatively connected to the source of compressedair 39 through a device 37 which responds to the control system 60 forcontrolling the flow of compressed air. The device 37 can be anunloading mechanism, a diverter valve, or other device capable ofselectively causing compressed air to flow from the source 39 to thereservoirs 50,50'. Mechanisms such as diverter valves are well-known inthe art. It will be apparent to those skilled in the art that the systemcan operate with any number of reservoirs and air actuated components.

FIG. 3 shows a detailed schematic representation of one embodiment ofthe present invention shown in block diagram form in FIG. 2. Referringto FIG. 3, the air compressor 36 is connected from an air compressoroutlet 38 to the first reservoir 50 at a first reservoir air inlet 52 byconduits 40 and 44 and to the second reservoir 50' at a second reservoirair inlet 52' by conduits 40 and 46. In another embodiment usingmultiple reservoirs, all of the reservoirs could be connected in series.It will be apparent to those skilled in the art that one-way valves maybe utilized in the actual implementation in order to maintain isolationof the reservoirs, thus preventing any air flow between the reservoirs.

The first reservoir 50 is connected by conduit 54 to the first set ofair-actuated components 56. The second reservoir 50' is connected byconduit 54' to the second set of air-actuated components 56'. In oneembodiment, one set of air-actuated components includes only servicebrakes of the tandem and trailer and the other set of air-actuatedcomponents includes at least parking brakes, windshield wipers and thetandem front service brakes. The pressurized air system 30, however, isnot limited to providing air to only these components.

As shown in FIG. 3, the air compressor outlet 38 can be connecteddirectly to the first reservoir 50 by conduits 40 and 44 and to thesecond reservoir 50' by conduits 40 and 46. Alternatively, the aircompressor outlet 38 can be connected directly to a supply reservoir,which is connected to the first and second reservoirs by respectiveconduits. In the prior art air pressure in the system is measured fromthe supply reservoir and the operation of the air compressor 36 iscontrolled responsive to the supply reservoir air pressure. The supplyreservoir, however, is not essential to the effective operation of thepresent invention, but may be included in the present invention to allowconversion from the prior art to the present invention (as shown in FIG.6, discussed more fully herein). The supply reservoir may also beutilized to provide sufficient air supply capacity for the pressurizedair system 30. The supply reservoir provides additional air supplycapacity for the pressurized air system 30. When converting prior art tothe present invention, it may be necessary to leave the supply reservoirfrom the prior art intact to maintain the system air supply capacity.Alternatively, larger air reservoirs of sufficient air supply capacitycould be used without the need for the additional air supply capacityprovided by the supply reservoir.

The control system, generally indicated by the components enclosed indashed line 60, consist of a first switch 65 and a second switch 65'that are operatively connected to the two reservoirs 50 and 50',respectively. It is to be understood, however, that the presentinvention performs reliably with only one reservoir and one switch aswell as with multiple reservoirs and corresponding multiple switches(i.e., one switch for each reservoir). An actuator 70 is also part ofthe control system 60, and is configured to respond to electric signalsgenerated by the two switches 65 and 65'.

The first reservoir 50 is connected to the first switch 65 at a firstswitch air inlet 59 by conduit 58. The second reservoir 50' is connectedto the second switch 65' at a second switch air inlet 59' by conduit58'. The switches 65 and 65' have diaphragms 64 and 64', respectively.The diaphragms 64 and 64' toggle between activated positions 64a and64a' and deactivated positions 64b and 64b', respectively, in responseto air pressure changes in their corresponding reservoirs 50 and 50'.The switches with diaphragms are commercially available and, therefore,are only schematically shown in the drawing. It will be apparent tothose skilled in the art that other switches can be utilized to generateelectric signals in response to air pressure differentials. For example,a sliding pole switch with a piston acting against a spring to forcemovement of a pole in response to changing air pressure, can beeffectively utilized.

The actuator is comprised of an electric valve setter 71 and a valve 72.The first switch 65 and the second switch 65' are connected in parallel,by electrically conductive leads 68 and 68' respectively, to theelectric valve setter 71. The electric valve setter 71 moves the valve72 between a first position 72a and a second position 72b. The electricvalve setter 71 can receive electric signals from both switches 65 and65'. FIG. 3 shows leads 68 and 68' joining at junction 69 and making oneconnection to the electric valve setter 71. However, each lead 68 and68' could be connected directly to the electric valve setter 71. In thepreferred embodiment shown in FIG. 3, the electric valve setter 71 is asolenoid. It will be apparent to those skilled in the art, however, thatother electrical components could be utilized to move the valve 72 inresponse to an electric signal.

Both the first switch 65 and the second switch 65' are also connected toa power source, generally indicated at 67, by electrically conductiveleads 66 and 66', respectively. It is to be understood that the powersource 67 generally represents whatever appropriate voltage is requiredfor energizing the switches 65 and 65', and the electric valve setter71. The power source 67 can be a battery which is also the batteryservicing the vehicle. Alternatively, the power source 67 can be acommon electrical bus bar located in the vehicle cab or otherappropriate power available to the control system.

FIG. 3 shows the first reservoir 50 connected by conduit 55 to the valve72 at a valve air inlet 77. However, any reservoir in the pressurizedair system 30 can be connected to the valve 72 in this manner.Furthermore, any air supply source, outside of the pressurized airsystem 30 as shown in FIG. 3, could be connected to the valve 72 in thismanner. The valve 72 also has a valve air outlet 74 through which aircan be released to the atmosphere outside of the pressurized air system30. In the first position 72a of the valve, the valve air outlet 74 isopen and the valve air inlet 77 is blocked. In the second position 72bof the valve, the valve air outlet 74 is closed and the valve air inlet77 is unblocked. The valve 72 is also connected to the unloadingmechanism 34 by conduit 32. Like the prior art, the unloading mechanism34 is attached to the air compressor 36 and controls the operation ofthe air compressor 36.

It will be appreciated by those skilled in the art that the actuator 70could be modified to mechanically actuate and disengage the compressor.For example, a solenoid could be directly connected to the unloadingmechanism 34. The solenoid could be configured and arranged tomechanically operate the unloading mechanism 34 in response to theelectric control signals from the switches 65 and 65'. Such amodification is within the scope of this invention.

FIG. 5 shows a schematic representation of the present invention of thepressurized air system 30 as it is installed in a vehicle or tractor,shown generally at 80. The vehicle has a cab 82, an engine compartment84, and wheels 86.1, 86.2, 86.3, and 86.4. The air compressor 36 isshown mounted to an engine 88 located in the engine compartment 84. In atypical embodiment, the air compressor 36 is connected to an engineintake manifold 89 for receiving air to compress. Not all compressors,however, receive air from an engine intake manifold. The first reservoir50 and the second reservoir 50' are shown located in the enginecompartment 84 for simplicity. However, these reservoirs are generallyhung from frame rails of the vehicle. The first reservoir 50 is shownconnected by conduit 54 to the rear wheels 86.3 and 86.4, for supplyingair to the rear wheel service brakes, represented as the first set ofair-actuated components 56 in FIG. 3. If the vehicle has an attachedtrailer, conduit 54 is also connected to every operational wheel of thetrailer. The second reservoir 50' is shown connected by conduit 54' tothe front wheels 86.1 and 86.2. Conduit 54' also connects the secondreservoir 50' to any other air-actuated components.

It will be apparent to those skilled in the art that the actual locationof air hose and electrical connections to the components in thepressurized air system can be made from many different locations. By wayof example, FIG. 5 shows conduit 58 from the first reservoir 50connected in parallel to an air gauge 83 and the first switch 65.Similarly, conduit 58' from the second reservoir 50' is connected inparallel to the air gauge 83 and the second switch 65'. In analternative embodiment, the first switch 65 and the second switch 65'can be connected directly to the air gauge at its air inputs forconduits 58 and 58', respectively. Also, the air gauge 83 is shown forillustrative purposes, and is unnecessary to the effective operation ofthe present invention. Therefore, the reservoirs 50 and 50' could beconnected directly to the switches 65 and 65' respectively.

The control system 60 is preferably located in the cab 82 of the vehicle80. FIG. 5 illustrates the switches 65 and 65' and the actuator 70mounted within the cab 82. It will be obvious to those skilled in theart that placement of the components of the pressurized air system canvary. For example, the actuator 70 and the switches 65 and 65' can bemounted anywhere on the vehicle.

FIG. 6 represents an alternative embodiment of a pressurized air system100 according to the present invention. Like the embodiment shown inFIG. 3, this embodiment utilizes a control system 130, operativelyconnected to an air compressor 106 for actuating and disengaging the aircompressor in response to air pressure in the pressurized air system100. In this embodiment, however, the control system 130 measures andresponds to air pressure in a supply reservoir 112, rather than airpressure in reservoirs directly connected to air-actuated components.The alternative configuration permits the use of only one switch 135,within the control system 130, for operative connection to the supplyreservoir 112. Referring to FIG. 6, the air compressor 106 is connectedfrom an air compressor outlet 108 to the supply reservoir 112 by conduit110. The supply reservoir 112 is connected to a first reservoir 120 byconduit 114 and to a second reservoir 120' by conduit 116. The firstreservoir 120 is connected by conduit 124 to a first set of air-actuatedcomponents 126. The second reservoir 120' is connected by conduit 124'to a second set of air-actuated components 126'.

The supply reservoir 112 is connected to the switch 135 at a switch airinlet 129 by conduit 113. The switch 135 has a diaphragm 134 whichtoggles between an activated position 134a and a deactivated position134b in response to air pressure changes in the supply reservoir 112,that flow through conduit 113 and into the switch 135. Preferably theswitch is of the same type as the switches 65 and 65', illustrated inthe embodiment shown in FIG. 3. The switch 135 is connected by anelectrically conductive lead 138 to an electric valve setter 141. Theelectric valve setter 141 moves a valve 142 to a first position 142a anda second position 142b in response to an electric signal received fromthe switch 135. In the preferred embodiment shown in FIG. 3, theelectric valve setter 141 is a solenoid. However, it will be apparent tothose skilled in the art that alternative electrical components may beutilized to move the valve 142.

The switch 135 is also connected to a power source, generally indicatedat 137, by electrically conductive lead 136, for generating an electricsignal when the diaphragm 134 toggles to the activated position 134a.Like the embodiment shown in FIG. 3, it is to be understood that thepower source 137 generally represents whatever appropriate voltage isrequired for energizing the switch 135 and the electric valve setter141.

FIG. 6 shows the supply reservoir 112 connected by conduit 115 to thevalve 142 at valve air inlet 147. However, the air supply from anyreservoir in the pressurized air system 100 can be connected to thevalve 142 in this manner. Furthermore, any air supply source, outside ofthe pressurized air system 100, could be connected to the valve 142 inthis manner. The valve 142 has a valve air outlet 144 through which aircan be released to the atmosphere outside of the pressurized air system100. In the first position 142a of the valve, the valve air outlet 144is open and the valve air inlet 147 is blocked. In the second position142b of the valve, the valve air outlet 144 is closed and the valve airinlet 147 is unblocked. The valve 142 is further connected by unloadingmechanism conduit 102 to an unloading mechanism 104. Like the prior art,the unloading mechanism 104 is attached to the air compressor 106 andcontrols the operation of the air compressor 106.

Operation

Referring to FIG. 2, generally, the control system 60 drives the aircompressor 36 to compress air and to supply compressed air to the firstreservoir 50 and the second reservoir 50' at system start-up and duringoperation when air pressure in either the first reservoir 50 or thesecond reservoir 50' has decreased to at least the predetermined minimumair pressure (P_(min)). The control system 60 drives the air compressor36 to stop compressing air when air pressures in both the firstreservoir 50 and the second reservoir 50' have increased to at least thepredetermined maximum air pressure (P_(max)).

Referring to FIG. 3, the first switch 65 and the second switch 65'receive air pressure from the first reservoir 50 and the secondreservoir 50' respectively, through the first switch air inlet 59 andthe second switch air inlet 59' respectively. The first switch 65measures air pressure in the first reservoir 50 and the second switch65' measures air pressure in the second reservoir 50'. FIG. 3 shows inschematic view the positions of the diaphragms 64 and 64' resulting fromchanging air pressures in their corresponding reservoirs 50 and 50'. Thefirst diaphragm 64 in the first switch 65, toggles between the activatedposition 64a and the deactivated 64b position as a result of airpressure changes in the first reservoir 50. The second diaphragm 64' inthe second switch 65', toggles between the activated position 64a' andthe deactivated 64b' position as a result of air pressure changes in thesecond reservoir 50'.

At system start-up and during operation when air pressure in the firstreservoir 50 decreases to at least the P_(min), the first diaphragm 64toggles to the activated position 64a. When the first diaphragm 64 is inthe activated position 64a, it touches the lead 68 and sends an electricsignal to the electric valve setter 71. The first diaphragm 64 remainsin the activated position 64a until air pressure in the first reservoir50 increases to at least the P_(max), at which time the first diaphragm64 toggles to the deactivated position 64b. When the first diaphragm 64is in the deactivated position 64b, no electric signal is sent to theelectric valve setter 71 from the first switch 65. The first diaphragm64 remains in the deactivated position 64b until air pressure in thefirst reservoir 50 decreases to at least the P_(min) again, at whichtime the first diaphragm 64 toggles to the activated position 64a andthe cycle continues.

In the preferred embodiment, the first switch 65 and the second switch65' are identical. The foregoing discussion of operation of the firstswitch 65 applies equally to the second switch 65', except the firstswitch 65 operates in response to air pressure in the first reservoir 50and the second switch 65' operates in response to air pressure in thesecond reservoir 50'. As will be appreciated by those skilled in theart, the switches may be configured to respond to air pressure inexactly the opposite manner. With appropriate wiring and solenoidconfiguration, the switches 65 and 65' could generate an electric signalwhen respective reservoir air pressure increased to at least the P_(max)and could cease generating signal when respective reservoir air pressuredecreased to at least the P_(min). The changed solenoid configurationwould cause the unloading mechanism 34 to hold open a popet valve (notshown) in the compressor when air pressure in both reservoirs increasedto P_(max) and to close the popet valve when air pressure in at leastone reservoir decreased to the P_(min).

Preferably, the switches 65 and 65' have the following P_(min) andP_(max) settings: P_(min) ≧90 pounds per square inch (psi); and P_(max)≧120 pounds per square inch (psi), where P_(min) <P_(max). An example ofsuch a switch is an Air Pressure Switch, Model Number PM-512K2-092NC,manufactured by Index Sensors & Controls, Inc. of Bellevue, Wash. TheIndex Sensors & Controls Air Pressure Switch has settings of P_(min)=97-99 psi and P_(max) =117-119 psi. The switches 65, 65' can bedesigned to accommodate any pressure settings, but the preferredembodiment complies with safety regulations for vehicles.

The electric valve setter 71 is electrically connected to the firstswitch 65 and the second switch 65' by leads 68 and 68' respectively.The electric valve setter 71 responds to the electric signals generatedby the switches 65 and 65' and controls the position of the valve 72.When the electric valve setter 71 receives an electric signal from atleast one of the first switch 65 and the second switch 65', the valve 72moves to the first position 72a. When no electric signal is received bythe electric valve setter 71 from any switch 65 or 65', then the valve72 moves to the second position 72b.

In the first position 72a the valve air outlet 74 is blocked from theatmosphere outside of the pressurized air system 30 and in the secondposition 72b the valve air outlet 74 is open to the atmosphere outsideof the pressurized air system 30. When the valve 72 is in the firstposition 72a, air freely flows from the unloading mechanism 34, throughconduit 32 and out of the valve air outlet 74 to outside of thepressurized air system 30. The release of air from the unloadingmechanism 34, actuates the air compressor 36, which then beginscompressing air and sending air through conduits 40, 44 and 46 to thefirst reservoir 50 and the second reservoir 50'. When the valve 72 is inthe first position 72a, the valve air inlet 77 is blocked and air doesnot flow from conduit 55 through the valve 72 and into the unloadingmechanism 34.

In the second position 72b of the valve 72, the valve air outlet 74 isclosed and air does not flow out of the valve air outlet 74 to outsideof the pressurized air system. The valve air inlet 77 is unblocked, andair flows from conduit 55 through the valve air inlet 77, throughconduit 32 and into the unloading mechanism 34. When the valve 72 is inthe second position 72b, the flow of air into the unloading mechanism 34disengages a compressor popet valve (not shown) which causes the aircompressor 36 to stop compressing air.

FIGS. 4(a) through 4(d) show schematically the operation of thepressurized air system 30, according to the embodiment of the presentinvention as shown in FIGS. 2 and 3, as the air pressures in thereservoirs 50 and 50' vary. For simplicity FIGS. 4(a)-4(d) do not showthe dashed line designating the control system 60.

FIG. 4(a) represents the system start-up of the present invention whenair pressure in the first reservoir 50, P₁, and air pressure in thesecond reservoir 50', P₁, are at least as low as the P_(min) (P₁≦P_(min)). The P₁ air pressure in the first reservoir 50 causes thefirst diaphragm 64 to toggle to the activated position 64a and to sendan electric signal to the electric valve setter 71. The P₁ air pressurein the second reservoir 50' causes the second diaphragm 64' to toggle tothe activated position 64a and to send an electric signal to theelectric valve setter 71. The electric signals from the switches 65 and65' cause the valve 72 to move to the first position 72a in which thevalve air inlet 77 is blocked so that no air passes from conduit 55through the valve air inlet 77 and to the unloading mechanism 34. Thevalve air outlet 74 is open such that air is released from the unloadingmechanism 34 through conduit 32 and out of the valve air outlet 74 tooutside of the pressurized air system 30. The release of air from theunloading mechanism 34 engages the air compressor 36, which beginscompressing air and sending the compressed air to the first reservoir 50and the second reservoir 50' through conduits 40, 44 and 46.

FIG. 4(a) also represents the present invention during other phases ofoperation. Such phases occur when air pressures in both reservoirs 50and 50' previously decreased to at least as low as the P_(min). Afterdecreasing to at least as low as the P_(min), and the switches 65 and65' moved to the activated positions 64a and 64a' respectively, airpressure in at least one of the reservoirs 50 or 50' then increased toan air pressure level higher than the P_(min), but still lower than theP_(max). In this situation, both switches 65 and 65' would be in theactivated positions 64a and 64a' respectively, even though one or bothof the reservoirs 50 or 50' had an air pressure level greater than theP_(min) but less than the P_(max).

FIG. 4(b) represents the present invention during operation when airpressure in the first reservoir 50, P₁, is at least as low as theP_(min) (P₁ ≦P_(min)), or when air pressure in the first reservoir 50,P₁, previously decreased to at least the P_(min) and is now greater thanthe P_(min) but is still less than the P_(max) (P_(min) <P₁ <P_(max)).Air pressure in the second reservoir 50', P₂, is at least as high as theP_(max) (P₂ ≧P_(max)), or air pressure in the second reservoir 50', P₂,previously increased to at least the P_(max) and is now less than theP_(max) but is still greater than the P_(min) (P_(min) <P₂ <P_(max)).During this phase, when air pressure in the first reservoir 50 decreasesto at least the P_(min), the first diaphragm 64 toggles to the activatedposition 64a and the first switch 65 sends an electric signal to theelectric valve setter 71. When air pressure in the second reservoir 50'increases to at least the P_(max), the second diaphragm 64' toggles tothe deactivated position 64b and no electric signal is generated fromthe second switch 65'. The electric signal from the first switch 65,however, causes the valve 72 to move to the first position 72a in whichthe valve air inlet 77 is blocked so that no air passes from conduit 55through the valve air inlet 77 and to the unloading mechanism 34. Thevalve air outlet 74 is open such that air is released from the unloadingmechanism 34 through conduit 32 and out of the valve air outlet 74 tooutside of the pressurized air system 30. The release of air from theunloading mechanism 34 engages the air compressor 36, which beginscompressing air and sending the compressed air to the first reservoir 50and the second reservoir 50' through conduits 40, 44 and 46.

FIG. 4(c) represents the present invention during operation when airpressure in the first reservoir 50, P₂, is at least as high as theP_(max) (P₂ ≧P_(max)), or air pressure in the first reservoir 50, P₂,previously increased to at least the P_(max) and is now less than theP_(max) but is still greater than the P_(min) (P_(min) <P₂ <P_(max)).Air pressure in the second reservoir 50', P₁, is at least as low as theP_(min) (P₁ ≦P_(min)), or air pressure in the second reservoir 50', P₁,previously decreased to at least the P_(min) and is now greater than theP_(min) but is still less than the P_(max) (P_(min) <P₁ <P_(max)).During this phase, when air pressure in the first reservoir 50 increasesto at least the P_(max), the first diaphragm 64 toggles to thedeactivated position 64b and no electric signal is generated from thefirst switch 65. When air pressure in the second reservoir 50' decreasesto at least the P_(min), the second diaphragm 64' toggles to theactivated position 64a and the second switch 65' sends an electricsignal to the electric valve setter 71. The electric signal from thesecond switch 65' causes the valve 72 to move to the first position 72ain which the valve air inlet 77 is blocked so that no air passes fromconduit 55 through the valve air inlet 77 and to the unloading mechanism34. The valve air outlet 74 is open and air is released from theunloading mechanism 34 through conduit 32 and out of the valve airoutlet 74 to outside of the pressurized air system 30. The release ofair from the unloading mechanism 34 engages the air compressor 36, whichbegins compressing air and sending the compressed air to the firstreservoir 50 and the second reservoir 50' through conduits 40, 44 and46.

FIG. 4(d) represents the present invention during operation when airpressure in the first reservoir 50, P₂, is at least as high as theP_(max) (P₂ ≧P_(max)), or when air pressure in the first reservoir 50previously increased to at least the P_(max) and is now less than theP_(max) but is still greater than the P_(min) (P_(min) <P₂ <P_(max)).Air pressure in the second reservoir 50', P₂, is also at least as highas the P_(max) (P₂ ≧P_(max)), or air pressure in the second reservoir50', P₂, previously increased to at least the P_(max) and is now lessthan the P_(max) but is still greater than the P_(min) (P_(min) <P₂<P_(max)). When air pressure in the first reservoir 50 increases to atleast the P_(max), the first diaphragm 64 toggles to the deactivatedposition 64b and no electric signal is generated from the first switch65. When air pressure in the second reservoir 50' increases to at leastthe P_(max), the second diaphragm 64' toggles to the deactivatedposition 64b' and no electric signal is generated from the second switch65'. When the electric valve setter 71 does not receive an electricsignal, the valve 72 moves to the second position 72b in which the valveair inlet 77 is unblocked. The valve air outlet 74 is closed so that airflows from conduit 55 through the unblocked valve air inlet 77, throughconduit 32 and into the unloading mechanism 34. The air then passes fromthe unloading mechanism 34 into the air compressor 36. The flow of airinto the unloading mechanism 34 disengages the compressor popet valve(not shown) which causes the air compressor 36 to stop compressing air.The system remains in this state until air pressure in at least one ofthe first reservoir 50 and the second reservoir 50' decreases to atleast the P_(min).

The operation of the pressurized air system 100 according to thealternative embodiment illustrated in FIG. 6, can be described withreference to FIG. 6. The operation of the switch 135 is identical to theoperation of the switches 65 and 65' previously described, and theoperation of the actuator 140 is identical to the operation of theactuator 70, also previously described. However, in the embodiment shownin FIG. 6, the switch 135 receives air pressure from the supplyreservoir 112 by conduit 113 at the switch air inlet 129. When the airpressure in the supply reservoir decreases to at least the predeterminedminimum air pressure (P_(min)), the diaphragm 134 toggles to theactivated position 134a and the switch 135 sends an electric signal tothe electric valve setter 141. The electric signal from the switch 135causes the valve 142 to move to the first position 142a in which thevalve air inlet 147 is blocked so that no air passes from conduit 115through the valve air inlet 147 and to the unloading mechanism 104. Thevalve air outlet 144 is open such that air is released from theunloading mechanism 104 through conduit 102 and out of the valve airoutlet 144 to outside of the pressurized air system 100. The release ofair from the unloading mechanism 104 engages the air compressor 106,which begins compressing air and sending the compressed air to thesupply reservoir 112, which then travels to the first reservoir 120 andthe second reservoir 120' through conduits, 114 and 116 respectively.

The diaphragm 134 remains in the activated position 134b until airpressure in the supply reservoir 112 increases to at least the P_(max),at which time the diaphragm 134 toggles to the deactivated position134b. When the diaphragm 134 is in the deactivated position 134b, noelectric signal is generated from the switch 135. When the electricvalve setter 141 does not receive an electric signal, the valve 142moves to the second position 142b in which the valve air inlet 147 isunblocked. The valve air outlet 144 is closed so that air flows from theconduit 115 through the unblocked valve air inlet 147, through conduit102 and into the unloading mechanism 104. The air then passes from theunloading mechanism 104 into the air compressor 106. The flow of airdisengages the air compressor 106 which stops compressing air. Thepressurized air system 100 remains in this state until air pressure insupply reservoir 112 decreases to at least the P_(min).

The control system 60 of FIG. 2 can utilize other means for controllingthe air compressor 36. For example, the control system can operate adiverter valve to control the compressor 36. When the air pressure in atleast one of the air reservoirs 50,50' has reached at least apredetermined minimum, the control system 60 will close the divertervalve so that the compressed air flows from the compressor 36 to the airreservoirs 50,50'. When the air pressure in both of the air reservoirs50,50' has reached at least a predetermined maximum, the control system60 opens the diverter valve so that compressed air is released from thecompressor 36, rather than flowing to the air reservoirs 50,50'. In suchan embodiment, the compressor 36 continually compresses air, with thecompressed air flowing to the air reservoirs 50,50' only when needed. Asshown in FIG. 7, the device 37, which can be an unloading mechanism, adiverter valve or the like, can be used to control a typical aircompressor as previously described herein or any other source ofcompressed air 39.

The scope of the present invention also covers an alternative embodimentusing microprocessors and air pressure sensors to monitor reservoir airpressure and thereby control compression of air by the air compressor.Such an embodiment could be implemented consistent with theconfiguration of FIG. 3, monitoring air pressure from each reservoirdirectly, or FIG. 6, monitoring air pressure solely from the supplyreservoir. Air pressure sensors would be configured to sense the airpressure in the appropriate reservoirs. The air pressure sensors wouldbe operatively connected to a microprocessor for generating a signalindicative of the sensed air pressure. The microprocessor would beoperatively connected to the air compressor and would respond to thesensed air pressure signal(s) by providing a control signal to actuateor disengage the air compressor. Such an embodiment is well within thescope of the present invention and could be configured using a varietyof electrical components.

The control system 60 of the present invention has many advantages. Theswitches 65 and 65' and the actuator 70 can be placed in any area of thevehicle, preferably in the cab which is advantageously removed from theengine and the air compressor 36. Placement in the cab insulates thecontrol system 60 from excessive vibration from the engine, dirt fromthe engine, extreme temperature fluctuations, moisture, and otherproblematic external parameters. The switches 65 and 65' each have onlyone (1) moving part and the actuator 70 is controlled by only one (1)electric valve setter 71. The small number of moving parts within thecontrol system 60 simplifies maintenance and troubleshooting and mostimportantly, increases reliability. In one embodiment of the presentinvention illustrated in FIGS. 2-4, air pressure is monitored directlyfrom the air reservoirs 50 and 50' to adjust the flow of compressed airthrough the pressurized air system 30, making the detection of low orhigh air pressure in the reservoirs 50 and 50' very accurate. In anotherembodiment illustrated in FIG. 6, air pressure is monitored from thesupply reservoir 112 to adjust the flow of compressed air through thepressurized air system 100, simplifying conversion from the prior art tothe present invention. Finally, existing prior art can be easilyconverted to any of the embodiments illustrated and/or described herein.

Although the present invention has been described with reference to thepreferred embodiments, those skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. Accordingly, it is intended that the scopeof the present invention only be limited by the scope of the claimswhich are appended hereto.

What is claimed is:
 1. A pressurized air system of the type having anair compressor which supplies compressed air to at least one reservoirwhen the air compressor is actuated, and wherein the reservoir deliverscompressed air to a set of air-actuated components, wherein theimprovement comprises a control system for controlling the aircompressor, the control system comprising:a. an actuator operativelyconnected to the air compressor, said actuator forcing compressed air toflow from the air compressor to the reservoir when air pressure in theair reservoir decreases to at least a predetermined minimum, and saidactuator interrupting the flow of compressed air from the air compressorto the reservoir when air pressure in the air reservoir increases to atleast a predetermined maximum; b. a controller operatively connected tosaid actuator for providing a control signal to said actuator, thecontrol signal indicative of air pressure in the air reservoir; c. saidactuator including:i. a valve having a first position and a secondposition with said actuator forcing compressed air to flow from the aircompressor to the reservoir when said valve is in said first positionand said actuator interrupting the flow of compressed air from the aircompressor to the reservoir when said valve is in said second position;and ii. an electric valve setter for moving said valve between the firstposition and the second position, said electric valve setter responsiveto the control signal.
 2. A pressurized air system according to claim 1wherein said actuator is a diverter valve.
 3. A pressurized air systemaccording to claim 1 wherein said actuator is an unloading mechanism. 4.A pressurized air system according to claim 1 wherein said controllercomprises a switch having:a. an activated position and a de-activatedposition; b. a switch air inlet connected to the reservoir with saidswitch shifted between said activated position and said de-activatedposition in response to a pressure of air admitted at said switch airinlet; and c. a valve lead electrically connected to said electric valvesetter for transmitting the control signal from said switch to saidelectric valve when said switch is in the activated position.
 5. Apressurized air system according to claim 4 wherein said switchcomprises a diaphragm, located inside said switch, for moving betweenthe activated position and the de-activated position in response to saidair pressure in the reservoir.
 6. A pressurized air system forcontrolling air-actuated components, the pressurized air systemcomprising:a. an air compressor having an air compressor outlet forcompressed air; b. at least one reservoir for compressed air with areservoir air inlet connected to the air compressor outlet and areservoir output connected to a set of air-actuated components; and c. acontrol system for controlling the flow of air from said air compressor,said control system comprising:i. an actuator operatively connected tosaid air compressor, said actuator forcing compressed air to flow fromsaid air compressor to said reservoir when air pressure in saidreservoir decreases to at least a predetermined minimum and saidactuator interrupting the flow of compressed air from said aircompressor to said reservoir when air pressure in said reservoirincreases to at least a predetermined maximum; and ii. a controlleroperatively connected to said actuator for providing a control signal tosaid actuator indicative of air pressure in said reservoir; d. saidactuator including:i. a valve having a first position and a secondposition with said actuator forcing compressed air to flow from said aircompressor to said reservoir when said valve is in said first positionand said actuator interrupting the flow of compressed air from said aircompressor to said reservoir when said valve is in said second position;and ii. an electric valve setter moving said valve between the firstposition and the second position, said electric valve setter responsiveto the control signal.
 7. A pressurized air system according to claim 6wherein said controller comprises a switch having:a. an activatedposition and a de-activated position; b. a switch air inlet connected tosaid reservoir with said switch shifted between said activated positionand said de-activated position in response to a pressure of air admittedat said switch air inlet; and c. a valve lead electrically connected tosaid electric valve setter for transmitting the control signal from saidswitch to said electric valve setter when said switch is in saidactivated position.
 8. A pressurized air system according to claim 6wherein said actuator is a diverter valve.
 9. A pressurized air systemfor controlling air-actuated components, the pressurized air systemcomprising:a. a source of compressed air having a source outlet forcompressed air; b. at least one reservoir for compressed air with areservoir air inlet connected to the source outlet and a reservoiroutput connected to a set of air actuated components; and c. a controlsystem for controlling said source, said control system comprising:i. anactuator operatively connected to said source, said actuator forcing theflow of compressed air from said source to said reservoir when airpressure in said reservoir decreases to at least a predetermined minimumand said actuator interrupting the flow of compressed air from saidsource to said reservoir when air pressure in said reservoir increasesto at least a predetermined maximum; and ii. a controller operativelyconnected to said actuator for providing a control signal to saidactuator indicative of air pressure in said reservoir; d. said actuatorincluding:i. a valve having a first position and a second position withsaid actuator forcing the flow of compressed air from said source tosaid reservoir when said valve is in said first position and saidactuator interrupting the flow of compressed air from said source tosaid reservoir when said valve is in said second position; and ii. anelectric valve setter moving said valve between the first position andthe second position, said electric valve setter responsive to thecontrol signal.
 10. A pressurized air system according to claim 9wherein said controller comprises a switch having:a. an activatedposition and a de-activated position; b. a switch air inlet connected tosaid reservoir with said switch shifted between said activated positionand said de-activated position in response to a pressure of air admittedat said switch air inlet; and c. a valve lead electrically connected tosaid electric valve setter for transmitting the control signal from saidswitch to said electric valve setter when said switch is in saidactivated position.
 11. A pressurized air system according to claim 9wherein said source of compressed air is an air compressor.
 12. Apressurized air system according to claim 11 wherein said actuator is adiverter valve.